Self-sealing wrapping material



United States Patent SELF-SEALING WRAPPING MATERIAL John F. Hechtman,Munising, Mich, assignor to The Munising Paper Company, Chicago, 11]., acorporation of Ohio No Drawing. Continuation of application Serial No.187,667, September 29, 1950. This application October 9, 1953, SerialNo. 385,271

13 Claims. (Cl. 117-68.5)

This invention relates to a wrapping material adapted for wrapping smallarticles such as a sandwich or other comestible, for example, and moreparticularly to a selfsealing wrapping material for wrapping acomestible to maintain its moisture content. In its preferred aspectsthe invention relates to a self-sealing wrapping material which isadapted to encase an article in the form of a closed envelope andthereby seal the article to not only maintain its moisture content butto protect the same against outside moisture, dust, gas and otherforeign matter.

Self-sealing wrapping material of the type to which the presentinvention relates are known. One such selfsealing wrapping materialcomprising a flexible porous paper backing having a self-sealing coatingof a cohesive, substantially non-adhesive material thereon is describedin United States patent application of Bertram L. Trillich, Serial No.125,973, filed November 7, 1949, now Patent No. 2,529,060. I havefoundthat when the backing is of a porous nature no special problems arise inthe application to, and the formation on, the backing of a suitableself-sealing material. When, however, the backing is of a non-porouscharacter problems arise at times. Thus for example, natural rubber isone of the most effective self-sealing materials for flexible porousbackings such as paper, but with a flexible non-porous backing materialsuch as cellophane, glassine paper, greaseproof paper and aluminum foil,natural rubber is not entirely suitable for at times it does not adheresutiiciently tenaciously to the non-porous backing. The adhesion betweenthe rubber and the backing is low. In consequence the rubber tends toseparate from the backing, especially when a seal is once made and thenbroken. In addition, delamination of a natural rubber film of cohesivematerial on a nonporous backing not infrequently takes place onstanding. In general, a wrapping material of a non-porous charac terhaving thereon a coating of natural rubber as the cohesive material, hasproven unsatisfactory because of adhesion failures between the rubberand the backing and because these wrapping materials have little, ifany, reseal value.

In contrast to natural rubber, polar synthetic rubbers have excellentadhesion to flexible, non-porous backing materials, but such rubbershave at times proven to be objectionable, self-adhering coatings forthese non-porous backings for two reasons. Some of these syntheticrubbers have not proven to be sufficiently cohesive at low pressures androom temperatures to meet commercial requirements, while others whichare sufficiently cohesive exhibited strong tendencies to adhere toordinary materials such as paper, cellophane, wood, glass, metal, andthe like. Because of these adhesive tendencies the wrapping materialsare sticky to the touch and are objectionable for this reason. They arefurther objectionable because when the wrapping material is used in rollform the roll tends to block. This means that the cohesive material hasadhered to the backing of the adjacent turn with e: F i- 45 rate i 2which it is in contact and cannot be unrolled without tearing of thesheet.

in accordance with the present invention 1 have prepared a self-sealingWrapping material having a non porous backing, which has none of theobjections noted above. This wrapping material is not tacky to the touchand will not block when rolled in roll form for dispensing purposes.This wrapping material may be sealed readily and rescaled many timeswithout delamination of the cohesive coating from the backing. Otheradvantages of the invention will be apparent from the following detaileddescription of the invention.

The wrapping material of the present invention consists essentially of apaper-thin flexible backing such as a flexible film, foil or sheet of anon-porous material carrying on one side thereof a flexible coating orfilm of self-adhering material which is substantially dry to the touchand substantially non-tacky but which is cohesive even under lightpressure, and yet which is for all practical purposes non-adhesive to asurface such as paper, cellophane, metal, wood, glass, etc., devoid ofsaid material.

The flexible non-porous backing sheet may be a film, sheet or foil ofcellophane, aluminum, glassine paper, greaseproof paper, a rubberhydrohalide such as rubber hydrochloride (Pliofilm), polyethylene,copolymers of polyvinyl chloride and polyvinyl acetate, copolymers ofpolyvinyl chloride and acrylonitrile, polyvinylidine chloride alone andin combination with polyvinyl chloride or with polyvinyl alcohol or withany other vinyl compounds capable of forming foils or films, celluloseacetate, cellulose nitrate and other cellulose derivatives, hard papers,specifically hard sized papers, which permit of no surface penetrationor very little surface penetration, and the like.

The self-adhering material which is used in accordance with the presentinvention is a composition containing a mixture of natural rubber and alow molecular weight (below 100,000) acrylic nitrile-butadiene copolymerwhich exhibits excellent adhesion to the aforesaid backing material, hasgood cohesive properties, and in the dry state has moderate adhesion toordinary materials such as paper, cellophane, metal and the like. Apreferred low molecular weight copolymer which may be used is acopolymer of a butadiene-1,3 hydrocarbon and an acrylic nitrile,particularly a copolymer made by the polymerization in aqueous emulsionof a monomeric mixture consisting of from 50 to 80% by weight ofbutadiene-l,3 and from 20 to 50% by weight of acrylonitrile,characterized by possessing a molecular weight below 100,000 and aMooney viscosity, as determined by the Mooney viscosimeter using the 1.5inch rotor after 4 minutes at 212 F., between 10 and 35, and alsocontaining from 5 to 50%, based on the weight of copolymer, of a rosinalcohol or a mixture of rosin alcohols. A suitable rosin alcohol may bethe technical mixture of hydroabietyl alcohols, sold under the trademarkAbitol by the Hercules Powder Company.

lt is important in accordance with the present invention that thenatural rubber and the synthetic rubber be combined in controlledproportions for otherwise the desired quick tack, film strength andminimum tendency to block or stick in a roll are not obtained. Ingeneral, the proportions of constituents necessary to obtain thesedesired results may vary from to 60% of natural rub her and 90% to ofthe synthetic rubber, based on the dry weight of the constituents. Thebest results are obtained when the proportions are maintained within thelimits of 20% to of natural rubber and 80% to of synthetic rubber, basedon the dry weight of the constituents.

The cohesive, substantially non-adhesive film is formed on the flexible,non-porous backing material by applying to the backing material acoating of an aqueous dispersion or latex of the synthetic rubber in anunvulcanized state in admixture in the desired proportions within therange noted above, with a conventional, commercially available,ammonium-stabilized, unvulcanized natural rubber latex, and drying thesame. The mixed latices may or may not contain an anti-oxidant for therubbers, as desired. The film of rubber deposited from these mixedlatices inherently has the desired cohesive, substantially non-adhesiveproperties, quick tack, film strength, and minimum tendency to block orstick when the coated backing sheet is rolled up in a roll form.

The mixed latices may have incorporated therewith varying small amountsof suitable wetting, spreading and penetrating agents. Thus, forexample, from 0.5% to 5%, on a dry weight basis, of a surface activeagent may be added to the mixed latices. Examples of suitable surfaceactive agents are sodium lauryl sulphate, sodium cetyl sulphate, thesodium salt of the dioctyl ester of sulfosuccinic acid (Aerosol OT), thesodium sulphate derivatives of 7-ethyl-2-methyl-undecanol-4 (Tergitol 4)and 3,9 diethyl tridecanol-6 (Tergitol-7), decyl benzine sodiumsulfonate (Santomerse S), and phenyl-para-toluene sulfonate. There mayalso be incorporated with the mixed latices varying small amounts, fromabout 0.5% to 5%, on a dry weight basis, of a resin which serves to addquick tack and cohesive strength to the film of mixed natural rubber andsynthetic rubber. A suitable resinous material for this purpose is thesodium resinate compound sold under the trademark Dresinate 213. Theremay also be added to the mixed latices varying small amounts ofthickening agents, from about 0.5% to 3%, on a dry weight basis.Suitable thickening agents are sodium alginate, borated casein andmethyl cellulose.

The cohesive, substantially non-adhesive material is applied to thebacking in the form of a film of the mixed rubbers which is preferablydeposited uniformly over the entire surface of the backing from themixed latices of these rubbers. The amount of material so deposited iscontrolled so that it is not adhesive but becomes cohesive only when anequal amount of the same material is brought into contact with it, suchas occurs in making a face-to-face seal in the process of wrapping anarticle with the wrapping material of the present invention. In general,from both the economical and functional standpoint, the quantity ofmixed synthetic rubber deposited as a uniform film on the flexible,non-porous backing material may vary from 0.10 lb./ 17 x 22-500 reamweight to 1.0 lb./ 17 x 22-500 ream weight. Somewhat less of the mixedrubbers may be used in the form of a deposited film, but this is notpreferred. Larger amounts of such deposited mixed rubbers may be used upto the point where the deposited film is definitely adhesive to theordinary materials such as paper, cellophane, metal and the like, butsuch larger amounts are not necessary and may even be wasteful of thematerial. It is to be appreciated that there may be specific mixtures ofthe synthetic rubber and the natural rubber, within the range ofproportions stated, for obtaining optimum results with specificflexible, non-porous backing sheets. Hence some experimentalformulations may be required for a specific backing sheet to achieveoptimum results.

The following is a desirable formulation of a cohesive, substantiallynon-adhesive material for application to glassine paper and for a hardsized paper:

Dry parts Copolymer 100 Natural rubber 50 Dresinate 213 3 The followingis a desirable formulation of a cohesive, substantially non-adhesivematerial for cellophane and aluminum foil:

Dry parts Copolymer 100 Natural rubber 35 Dresinate 213 1 Borated casein2 The copolymer referred to in each of the above formulations is thespecific low molecular weight butadiene- 1,3-acrylonitrile copolymerused in the form of an approximately 35% solids content aqueous latex.Other butadiene-1,3 hydrocarbon and an acrylic nitrile copolymer havinga molecular weight below 100,000 may be used in lieu of the specificcopolymer of the illustrative examples. In connection with theseillustrative examples it is to be noted that they are preferred examplesand that the proportions of the rubbers may be varied as noted above andthe tackifying agent (Dresinate 213) and the thickening agent (beratedcasein) may be omitted, if desired.

Where the mixture of the synthetic rubber and the natural rubberapproach the upper limit of the range of proportions of the mixture ofrubbers, namely 90% of synthetic rubber and 10% of natural rubber, on adry weight basis, there is some slight tendency toward roll blocking,particularly in the case of an aluminum foil backing sheet. In the caseof aluminum foil backing sheets, as well as other flexible, non-porousbacking sheets, it may be desirable to provide a release coat of asuitable material on the back of the mixed rubber-coated backing sheet.Very light applications of paraflin wax or microcrystalline wax on theback of the backing sheets have been found to be very effective releaseagents which prevent roll blocking tendency. These waxes may be appliedto the back of the backing sheets either as flexible films depositedfrom aqueous emulsion, from solvent solution, or by application of thesematerials in molten form.

The use of the wrapping material of the present invention may beillustrated by way of the wrapping of a sandwich. The sandwich is placedon the cohesive, substantially non-adhesive coating of a piece of aWrapping sheet adjacent one end of the sheet and within the boundariesthereof. The opposite end of the wrapping sheet is then folded over thesandwich so that the marginal portions of the self-adhering coating ofthe folded sheet are in opposed relationship on three sides of thesandwich. A light pressure is then applied to the opposed surfaces ofthe self-adhering material by runnnig the fingers lightly around themarginal portions of the folded wrapping sheet, thereby sealing thesheet about the sandwich. Due to the fact that the mixed rubber coatingis not adhesive, it does not adhere to the sandwich. The seal formed asdescribed may be readily broken without effecting delamination of themixed rubber coating and the sheet may be used again as described aboveor in other manners, as desired.

The present application is a continuation of the parent applicationSerial No. 187,667, filed on September 29, 1950.

Having thus described the invention what I claim as new and desire tosecure by Letters Patent is:

1. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber and a copolymer of from 50 to by weight of abutadiene-1,3 hydrocarbon and from 20 to 50% by weight of an acrylicnitrile having a molecular weight below 100,000, in the proportion of 10to 60% of natural rubber and to 40% of the copolymer, on a dry weightbasis.

2. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber and a copolymer of from 50 to 80% by weight ofabutadiene-lj hydrocarbon and from 20 to 50% by weight of an acrylicnitrile having a molecular weight below 100,000, in the proportion of to60% of natural rubber and 90 to 40% of the copolymer, on a dry weightbasis, and having on the other surface thereof an exposed flexible Waxfilm.

3. As a new article of manufacture, a sheet of selfsealing Wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article com prising a thin, flexible sheet of a non-porousmaterlal having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber and a copolymer of from 50 to 80% by weight ofbutadiene-1,3 and from to 50% by weight of acrylonitrile having amolecular weight below 100,000, in the proportion of 10 to 60% ofnautral rubber and 90 to of the copolymer, on a dry weight basis.

4. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber, a copolymer of from to 80% by weight of butadiene-l,3and from 20 to 50% by weight of acrylonitrile having a molecular weightbelow 100,000, and a rosin alcohol in the amount of from 5 to 50%, basedon the weight of the copolymer, the proportion of natural rubber andcopolymer in the mixture varying from 10 to of the former to 90 to 40%of the latter, on a dry weight basis.

5. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of glassine paperhaving on one surface thereof an exposed flexible film of a cohesive,substantially non-adhesive material comprising a mixture of naturalrubber and a copolymer of from 50 to by weight of a butadiene-1,3hydrocarbon and from 20 to 50% by weight of an acrylic nitrile having amolecular weight below 100,000 in the proportion of 10 to 60% of naturalrubber and 80 to 40% of the copolymer, on a dry weight basis.

6. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article cornprising a thin, flexible sheet of greaseproofpaper having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber and a copolymer of from 50 to 80% by weight of abutadiene-1,3 hydrocarbon and from 20 to 50% by weight of an acrylicnitrile having a molecular weight below 100,000, in the proportion of 10to 60% of natural rubber and to 40% of the copolymer, on a dry weightbasis.

'7. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of cellophanehaving on one surface thereof an exposed flexible film of a cohesive,substantially non-adhesive material comprising a mixture of naturalrubber and a copolymer of from 50 to 80% of butadiene-l,3 hydrocarbonand from 20 to 50% by weight of an acrylic nitrile having a molecularweight below 100,000, in the proportion of 10 to 60% of natural rubberand 90 to 40% of the copolymer, on a dry weight basis.

8. As a new article of manufacture, a sheet of selfsealing Wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of aluminum havingon one surface thereof an exposed flexible film of a cohesive,substantially non-adhesive material comprising a mixture of naturalrubber and a copolymer of from 50 to 80% by weight of a butadiene-1,3hydrocarbon and from 20 to 50% by weight of an acrylic nitrile having amolecular weight below 100,000 in the proportion of 10 to 60% of naturalrubber and 90 to 40% of the copolymer, on a dry weight basis.

9. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of hard sized paperhaving on one surface thereof an exposed flexible film of a cohesive,substantially non-adhesive material comprising a mixture of naturalrubber and a copolymer of from 50 to 80% by weight of a butadiene-l,3hydrocarbon and from 20 to 50% by Weight of an acrylic nitrile having amolecular weight below 100,000, in the proportion of 10 to 60% ofnatural rubber and 90 to 40% of the copolymer, on a dry weight basis.

10. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial of the class consisting of greaseproof paper, cellophane,aluminum, hard sized paper and glassine paper, having on one surfacethereof an exposed flexible film of a co hesive, substantiallynon-adhesive material comprising a mixture of natural rubber, acopolymer of from 50 to 80% by Weight of butadiene-l,3 and from 20 to50% by Weight of acrylonitrile having a molecular Weight below 100,000,and a rosin alcohol in the amount of from S to 50%, based on the Weightof the copolymer, the proportion of natural rubber and copolymer in themixture varying from 10 to 60% of the former to 90 to 40% of the latter,on a dry weight basis.

11. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber, a copolymer of from 50 to 80% by weight of butadiene-l,3and from 20 to 50% by weight of acrylonitrile having a molecular weightbelow 100,000, and a rosin alcohol in the amount of from 5 to 50%, basedon the weight of the copolymer, the proportion of natural rubber andcopolymer in the mixture varying from 10 to 60% of the former to 90 to40% of the latter, on a dry weight basis, and having on the surfacethereof an exposed flexible wax film.

12. As a new article of manufacture, a sheet of selfsealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber, a copolymer of from 50 to 80% by weight of butadiene-l,3and from 20 to 50% by weight of acrylonitrile having a molecular weightbelow 100,000, a rosin alcohol in the amount of from 5 to 50%, based onthe weight of the copolymer, and a resin which serves to add quick tackand cohesive strength to the film and is in the amount of from 0.5 to5%, based on the Weight of the mixture of natural rubber and copolymer,the proportion of natural rubber and copolymer in the mixture varyingfrom 10 to 60% of the former to 90 to 40% of the latter, on a dry Weightbasis.

13. As a new article of manufacture, a sheet of self sealing wrappingmaterial adapted completely to encase an article and thereby seal thesame, said article comprising a thin, flexible sheet of a non-porousmaterial having on one surface thereof an exposed flexible film of acohesive, substantially non-adhesive material comprising a mixture ofnatural rubber and a copolymer of from 50 to 80% by weight of abutadiene-l,3 hydrocarbon and 7 8 from 20 to 50% by weight of an acrylicnitrile, said References Cited in the file of this patent copolymerbeing characterized by having a molecular NITED TATES PATENT weightbelow 100,000 and a Mooney viscosity, as de- U S S termined by means ofthe Mooney viscosirneter using the 2,357,662 im P 1944 1.5 inch rotorafter 4 minutes at 212 F., between 10 5 2,529,060 Tnlhch 1950 2,535,852Hatfield et a1 Dec. 26, 1950 and 35, in the proportion of 10 to 60% ofnatural 111bber and 90 to 40% of the copolyrner, on a dry weight basis.

2. AS A NEW ARTICLE OF MANUFACTURE, A SHEET OF SELFSEALING WRAPPINGMATERIAL ADAPTED COMPLETELY TO ENCASE AN ARTICLE AND THEREBY SEAL THESAME, SAID ARTICLE COMPRISING A THIN, FLEXIBLE SHEET OF A NON-POROUSMATERIAL HAVING ON ONE SURFACE THEREOF AN EXPOSED FLEXIBLE FILM OF ACOHESIVE, SUBSTANTIALLY NON-ADHESIVE MATERIAL COMPRISING A MIXTURE OFNATURAL RUBBER AND A COPOLYMER OF FROM 50 TO 80% BY WEIGHT OF ABUTADIENE-1,3 HYDROCARBON AND FROM 20 TO 50% BY WEIGHT OF AN ACRYLICNITRILE HAVING A MOLECULAR WEIGHT BELOW 100,000, IN THE PROPORTION OF 10TO 60% OF NATURAL RUBBER AND 90 TO 40% OF THE COPOLYMER, ON A DRY WEIGHTBASIS, AND HAVING ON THE OTHER SURFACE THEREOF AN EXPOSED FLEXIBLE WAXFILM.